The red blood cells or erythrocytes in donor blood have a certain life span. Actually, human blood contains more or less equal portions of red blood cells of ages between about 0 and 120 days. Thus, in any given sample, there is a certain percentage of younger blood cells or so-called neocytes and a certain percentage of older cells call gerocytes. Also, human blood contains a relatively large amount of iron, on the order of 108 mg/dl of red cells, the iron content being relatively uniform regardless of the average cell age of the blood sample. Therefore, it is desirable to transfuse patients with younger blood cells in order to minimize the number of required transfusions, thereby minimizing the amount of iron introduced into the patient's body. It has also been recognized that the older red cells in donor blood are more dense than the younger ones. Using this knowledge, attempts have been made to separate the red cells in a donor sample according to their densities so as to segregate the younger cells or neocytes from the older cells or gerocytes.
The usual technique for separating whole blood in accordance with the densities of the blood fractions is to place the blood sample in a container and spin the container about an axis perpendicular to the container axis at a high speed to subject the container contents to a centrifugal force on the order of 2,000 G. The force exerted on the blood sample causes the heaviest, most dense blood fractions such as the red cells to accumulate at the end of the container distal to the spin axis, while the less dense fractions, such as the blood plasma, accumulate at zones in the container progressively closer to the spin axis. Typical apparatus for effecting density separation of blood fractions by centrifuging are disclosed in the following U.S. Pat. Nos.: 3,064,647, Earl; 3,935,113, Ayres; 3,750,645, Bennet et al.: 3,945,928, Ayres; 3,800,947, Smith; 4,187,861, Heffernan; 3,887,464, Ayres; 4,189,385, Greenspan; 4,268,393, Persidsky et al.
Relatively recently, a new technique described in U.S. Pat. No. 4,416,778 owned by the assignee of the present application, has been developed for separating the components of a liquid, including blood, according to their densities. In that apparatus, the sample liquid is placed in a first chamber and centrifuged at a high speed so as to distribute the liquid components in that chamber along a density continuum. Following that high speed centrifuging step, the liquid components in the first chamber are partitioned by transferring to a second chamber only those components beyond a selected partition line in the density continuum established in the first chamber so that the components in the two chambers are separated by density and can be used independently.
The apparatus disclosed in that patent for separating the blood components comprises two flexible bags connected by a tube, with the bags being mounted to two coupling sections which are releasably connected together during the separation process. That patented apparatus also includes valve structure for controlling the flow of fluid between the two chambers during the separation process.
While that apparatus separates blood and other liquids by density precisely and effectively, it is not as easy to manufacture and use as might be desired, primarily because of the requirement to mechanically couple together the two flexible bags in which the liquid sample is separated. The coupling components also add to the overall cost of the apparatus. Also, special seals and/or gaskets must be provided between the bags and the coupling components to provide the required valving between the two bags. Furthermore, those seals must be able to withstand the very high fluid pressures developed when the apparatus is spun at the very high speeds required to develop the density gradient in the liquid sample.